Water resources and vegetation jointly affect almost every aspect of nature and society, such as geomorphology, biodiversity, local climate, settlement, and so on. However, our understanding of their dependency relation is incomplete, which is merely on the unidirectional impact of a single water resource on vegetation. Inversely, vegetation productivity could feed back water resources by directly affecting evapotranspiration and indirectly regulating precipitation. The bidirectional influencing mechanism between global water resources and vegetation productivity is still unknown. This study focused on revealing the bidirectional dependency relation between water resources and vegetation productivity using multi-source data and causality modeling. Our analysis showed that the unidirectional dependence of vegetation on water resources, the unidirectional dependence of water resources on vegetation, and their bidirectional dependence at the global scale accounted for 40.9 %, 12.4 %, and 46.8 %, respectively. Moreover, different types of water resources and vegetation perform varying degrees of bidirectional dependency. For instance, precipitation influences 64.9 % of the vegetation in a unidirectional way, while soil moisture, surface runoff, and groundwater interact with vegetation at the level of 74.6 %, 44.8 %, and 45.6 %, respectively. Similarly, the bidirectional dependency between forest (54.5 %) and water resources was usually higher than that of cultivated land (45.9 %) and grassland (44.5 %), due to different transpiration and water interception abilities. It has great significance on water resources management, vegetation greening, and understanding of terrestrial ecological water circulation systems in the context of global climate change by quantifying the interaction mechanism between various water resources and vegetation productivity in this study.

中文翻译：

---

全球水资源与植被生产力的双向依赖

水资源和植被共同影响着自然和社会的几乎各个方面，如地貌、生物多样性、当地气候、聚落等。然而，我们对其依赖关系的认识并不完整，仅仅停留在单一水资源对植被的单向影响上。相反，植被生产力可以通过直接影响蒸散量和间接调节降水来反馈水资源。全球水资源与植被生产力之间的双向影响机制尚不清楚。本研究的重点是利用多源数据和因果关系模型揭示水资源与植被生产力之间的双向依赖关系。分析表明，全球尺度植被对水资源的单向依赖、水资源对植被的单向依赖和双向依赖分别占40.9%、12.4%和46.8%。此外，不同类型的水资源和植被表现出不同程度的双向依赖。例如，降水以单向方式影响64.9%的植被，而土壤湿度、地表径流和地下水与植被的相互作用程度分别为74.6%、44.8%和45.6%。同样，由于蒸腾和截水能力不同，森林（54.5%）与水资源的双向依赖通常高于耕地（45.9%）和草地（44.5%）。本研究通过量化各种水资源与植被生产力之间的相互作用机制，对于全球气候变化背景下的水资源管理、植被绿化以及认识陆地生态水循环系统具有重要意义。